HTML DOM classList attribute

Each node in the page DOM has a classList object. Programmers can use the methods inside to add, delete, and modify CSS classes on the node. Using classList, programmers can also use it to determine whether a certain node is assigned a certain CSS class.

Add class(add)

document.getElementById("myp").classList.add("mystyle");

Add multiple classes for

elements:

document.getElementById("myp").classList.add("mystyle", "anotherClass", "thirdClass");

Remove class(remove)

Use remove Method, you can delete a single CSS class:

document.getElementById("myp").classList.remove("mystyle");

Remove multiple classes:

document.getElementById("myp").classList.remove("mystyle", "anotherClass", "thirdClass");

Switch class (toggle)

The function of this method is that when the myp element is on If this CSS class does not exist, it will add this CSS class; if the myp element already has this CSS class, it will delete it. It's a reversal operation.

document.getElementById("myp").classList.toggle("newClassName");

myp.classList.toggle('myCssClass'); //现在是增加
myp.classList.toggle('myCssClass'); //现在是删除

Whether there is a class (contains)

Check whether it contains a certain CSS class:

var x = document.getElementById("myp").classList.contains("mystyle");

The result is true or false.

length attribute

Returns the number of classes in the class list.
Check how many class names the

element has:

var x = document.getElementById("myp").classList.length; //3

Get all the class names of the

element:

<p>I am a p element</p>

var x = document.getElementById("myp").classList;

item(index)

Return the index value of the class name in the element. Index values ​​start from 0. If the index value is outside the range, null is returned
Get the first class name of the

element (index is 0):

var x = document.getElementById("myp").classList.item(0); //mystyle

Browser support

However, IE9 and previous versions of IE9 do not support this attribute. The following code can make up for this regret: (from netizen code)

if (!("classList" in document.documentElement)) {  
        Object.defineProperty(HTMLElement.prototype, 'classList', {  
            get: function() {  
                var self = this;  
                function update(fn) {  
                    return function(value) {  
                        var classes = self.className.split(/\s+/g),  
                            index = classes.indexOf(value);  
                          
                        fn(classes, index, value);  
                        self.className = classes.join(" ");  
                    }  
                }  
                  
                return {                      
                    add: update(function(classes, index, value) {  
                        if (!~index) classes.push(value);  
                    }),  
                      
                    remove: update(function(classes, index) {  
                        if (~index) classes.splice(index, 1);  
                    }),  
                      
                    toggle: update(function(classes, index, value) {  
                        if (~index)  
                            classes.splice(index, 1);  
                        else  
                            classes.push(value);  
                    }),  
                      
                    contains: function(value) {  
                        return !!~self.className.split(/\s+/g).indexOf(value);  
                    },  
                      
                    item: function(i) {  
                        return self.className.split(/\s+/g)[i] || null;  
                    }  
                };  
            }  
        });  
    }

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